This invention relates generally to drive apparatus associated with vehicle accessories or the like. More particularly it relates to a speed and temperature responsive clutch for controlling the fan associated with the cooling system of an internal combustion engine.
Power losses would be significant if a fan were driven directly by a vehicle engine, as the power input for the fan is an exponential function of its rotational speed. Furthermore, at high speeds the fan would deliver more air than is required for cooling the engine. This would lead both to excessive cooling and objectionable noises.
In order to avoid these disadvantages, it has been suggested that a separate electric fan motor be provided, or that the fan itself have adjustable blades. It has also been suggested that a viscous clutch connection be provided between the engine and the fan. These suggestions generally have technical, operational or price disadvantages.
A mechanical friction clutch also has been suggested for use in driving a cooling system fan. However, where it is necessary or desirable that such a clutch be both speed and temperature responsive, it has in general proven to be impractical due to the structural relationships which are necessary for the provision of this automatic feature.
There remains a need in the art for drive apparatus which is both speed and temperature responsive, which operates automatically, and which is simple, reliable and inexpensive.